Design of a CMOS charge pump for high-performance phase-locked loop

In conventional CMOS charge pump circuits, there are some current mismatching characteristics which result in a phase offset in phase-locked loop circuits. This paper presents a new charge pump circuit after detailed analysis of the current mismatch problem. It combines an error amplifier with reference current sources to achieve good current matching characteristics and lower phase noises, and at the same time it can eliminate charge sharing by using charge removal transistors. The circuit was designed by chartered 0.35 um CMOS technology and simulated by Spectre tools. Simulation results show that the good current matching characteristics can be obtained with the proposed designing scheme.